In a lithography printing process, one or more printing plates are used to transfer ink to a printing substrate, with one plate for every ink composition used. A lithography plate has two regions: an oleophilic image area for receiving an oil-based ink and an oleophobic non-image area for receiving a water-based, non-imaging solution, known in the art as a "fountain" solution. During the printing process, the ink and fountain solution are applied to a printing plate and allowed to gravitate to their respective areas. The ink can be transferred directly to the substrate or it can be transferred to an intermediate "blanket" cylinder and subsequently transferred to the substrate, the latter being known in the art as offset lithography printing.
As with other printing inks, lithography printing inks are designed according to several criteria, including the desired visual characteristics of the printed material, the printing process which will be used, the drying conditions of the ink, the substrate to which the ink must adhere, and the wear resistance of the ink. While an ink may include various pigments to achieve a desired visual effect, an ink may also be designed to achieve other visual effects, such as a gloss or matte (dull) effect. A gloss effect occurs when incident light is reflected and a matte effect occurs when incident light is scattered. A popular visual effect is a combination matte-gloss contrast finish, which is particularly popular for magazine, book, and periodical covers. In this case, the matte and gloss coatings, both of which are preferably transparent, are printed over the pigmented ink coatings, if present.
To achieve a combination matte-gloss contrast finish according to present lithography printing methods, a substrate is first printed with a matte ink composition in selective areas where a matte effect is desired, after which, a gloss ink composition is printed onto the substrate in selective areas where a gloss effect is desired. The matte and gloss coatings normally do not overlap. While the matte and gloss coatings can be applied immediately following application of any pigmented ink(s), it is preferable to apply the matte and gloss coatings after the underlying coatings have dried. Nonetheless, in either case this process produces only a moderate contrast between the matte and gloss surfaces.
To achieve a superior matte-gloss contrast finish, another process has developed in which the substrate is first coated with a plastic matte film lamination. Because inks do not readily adhere to plastic films, a specialized gloss ink is used wherein the ink is selectively "spot" coated thereon and cured to the matte surface via ultra-violet (UV) radiation. Although this UV process produces a greater matte-gloss contrast than that seen from the offset lithography process, the gloss coating is not very durable and has a tendency to detach from the matte surface if the coated substrate is stressed, for example, by folding or creasing. Moreover, UV curing processes require specialized equipment (e.g. photopolymer plates or silk screens) and procedures that are both time consuming and expensive. Consequently, most lithography printing companies cannot afford the specialized UV equipment and must send their products to a printing company having the specialized UV equipment for application of the gloss coating, a detour which substantially increases production time and costs.
Other problems with the UV process includes that the photopolymer plates and silk screens are very coarse and it is extremely difficult to print fine detail. Accordingly, the detail available with the UV process is substantially inferior than that available with lithography printing. Also, with silk screens, it is difficult to regulate the amount of UV coating that is being applied to the sheet. Finally, since the UV process is somewhat different than the lithographic process, it is difficult to achieve proper registration between the gloss coating and the graphics that have been lithography printed on the substrate.
Accordingly, what is needed is a novel ink composition and method of use which overcome the problems in the prior art and which provide a superior matte-gloss contrast finish without the need for specialized UV equipment and procedures, wherein the overlay finish coat will not detach from the base finish coat when stressed.